1. Field of the Invention
The present invention relates generally to the production of bent or curved glass sheets, and more particularly to an articulated male press bending member embodying means for shifting the configuration of selected portions of its shaping surface between alternate positions.
2. Description of the Prior Art
Bent or curved sheets of glass are commonly employed as glazing closures in automotive vehicles. In order to conform to the styling of the vehicle and to properly fit within a designated opening within the vehicle body, it is necessary that the glass sheets must be bent to precisely defined curvatures. It is also necessary in order to comply with stringent Federal standards and to be aesthetically acceptable, that the bent sheets be relatively free of optical defects that might tend to interfere with vision therethrough. In accordance with Federal standards, such bent automotive glass is generally of two types, that is, tempered monolithic units acceptable for use as side lights and backlights, and laminated units required for use as windshields.
Production of the former generally includes heating pretrimmed flat sheets of glass to their softening temperature, bending the heated sheets individually to a desired curvature between a pair of complementarily shaped press members, and then rapidly chilling the bent sheets in a controlled manner to a temperature below the annealing range to produce thermally induced tempering of the glass. In producing the latter, two sheets of flat glass are heated to their softening point and bent to a matching or nesting configuration, and then gradually cooled in a controlled manner to a temperature below their annealing range so that the cooled sheets are in annealed condition. The sheets are then laminated, one to either surface of a plastic interlayer as of polyvinyl butyral.
Traditionally, glass sheets for laminated units were bent in pairs on a gravity mold having a peripheral shaping rail, to insure that the pair would match or nest properly so as to permit lamination to a thin interlayer. Such gravity bending was time consuming and costly, and while the paired sheets would bend reasonably well in the longitudinal direction about their transverse axis, they did not consistently develop the desired cross bend. In other words, they did not develop the desired curvature in the transverse direction, about their longitudinal axis, for sheets with compound curvature. More recently, sheets for laminated units have been individually press bent to the desired curvature between a pair of complementarily shaped press members, and then paired for lamination to a plastic interlayer.
In order to achieve the desired curvature while minimizing the area of contact between the mold surfaces and the glass in press bending, the male mold member has conventionally been constructed with a solid or continuous shaping surface adapted to engage the entire surface of the sheet. The female mold member comprises an outline or ring-type shaping surface which engages only the marginal edge portions of the sheet. Such male molds were traditionally formed of metal or cast refractory material. More recently, in order to provide for adaptation of the male mold to production of parts having somewhat different curvatures and to correct distortions which may develop during prolonged use, so called adjustable continuous-surface molds have been developed. Such molds generally comprise a shaping element including a flexible, resilient body having affixed to its underside at spaced intervals a plurality of adjustable support members. By appropriately adjusting the support members, the precise desired curvature may thus be imparted to the shaping element.
It has been found in press bending certain parts that better results are achieved if slightly greater pressure is applied to the glass in certain regions by the male mold member as the male and female mold sections press the heated sheet therebetween. This is particularly true in the bending of sheets for lamination as automotive windshields wherein the inboard and outboard lights, that is, the light facing the interior of the vehicle and the light facing the exterior, respectively, assume slightly different radii of curvature as the two are laminated to the plastic interlayer. Likewise, in bending lights for electrically conducting windshields, which include bus bars applied to the surface at the end of a sheet to be bent and thus create a temperature differential between the end or pillar area and the central portion of the sheet, different pressures may be required to achieve the same approximate radius of curvature as with sheets not having the bus bar. While the aforementioned adjustable continuous surface molds represent a significant improvement over previous solid molds insofar as they permit modification of the surface contour to achieve desired results, they are not adapted for rapid cycling between alternative modes as found desirable, for example, in bending the two individual sheets of a pair to be laminated.